Method and apparatus for differentiated paging channel selection

ABSTRACT

Disclosed is a method and apparatus to manage selection of a paging channel in a wireless communication system. When a mobile station powers on in a coverage area having multiple paging channels, the mobile station may apply a hashing algorithm keyed to the mobile station&#39;s identifier, to select a paging channel on which to idle. On the other hand, when the mobile station moves from a coverage area having a number of paging channels into a neighboring coverage area having a different number of paging channels, the mobile station may by rote idle on a default paging channel in the neighboring coverage area. In this way, the mobile station can help to avoid an access handoff failure that may arise from the mobile station being busy hashing onto a paging channel when the network transmits an access response message to the mobile station.

BACKGROUND

In a typical cellular wireless communication system, an area is dividedgeographically into a number of wireless coverage areas (e.g., cells andcell sectors), each defined by a radio frequency (RF) radiation patternfrom a respective base station. One or more base stations of the systemmay then be coupled with other network infrastructure, such as a basestation controller, switch, and/or gateway, which may control aspects ofbase station operation and may provide connectivity with one or moretransport networks such as the Public Switched Telephone Network and/orthe Internet for instance. When a mobile station, such as a cellulartelephone, personal digital assistant, pager, or appropriately equippedcomputer, for instance, is positioned in a wireless coverage area, themobile station may then communicate via an RF air interface with theserving base station and thereby establish communication with otherserved mobile stations or with entities on one or more connectedtransport networks.

In general, the air interface in each wireless coverage area of such asystem is divided into a number of channels for carrying bearer traffic(e.g., voice and other user data) and control data between the basestation and served mobile stations. The channels that carry data fromthe base station to served mobile stations are considered “forward link”channels, and the channels that carry data from served mobile stationsto the base station are considered “reverse link” channels. Depending onthe wireless technology used, the air interface can be divided intothese channels through code division multiplexing (with each channeldefined by modulation with a specific code), time division multiplexing(with each channel defined as a segment of time), frequency divisionmultiplexing (with each channel defined by modulation with a specificfrequency), and/or some other mechanism.

In terms of control channels, the forward link of each wireless coveragearea may define one or more overhead channels through which the basestation may generally broadcast system parameter information for use byserved mobile stations, and the forward link may further define one ormore paging channels through which the base station may transmit controlchannel messages typically targeted to specific mobile stations. Inturn, the reverse link of each wireless coverage area may define one ormore access channels through which served mobile stations can transmitto the base station requests to initiate calls (e.g., voice calls ordata communication sessions) and responses to control channel messagesreceived from the base station.

The wireless coverage areas (e.g., cell sectors) in a typical system maybe grouped into paging zones to help the system determine where to pagea mobile station. An overhead message broadcast in each coverage areamay specify the coverage area's paging zone, so that served mobilestations can detect when they move from one paging zone to another. Inpractice, when a mobile station initially powers on in a given coveragearea, the mobile station may register with the network by transmitting aregistration message via an access channel to the network, so that thenetwork will know the paging zone in which the mobile station islocated. In turn, when the mobile station moves into a new paging zone,the mobile station may then newly register with the network, to notifythe network of the mobile station's new paging zone. When the networkseeks to page the mobile station, the network may then transmit the pagemessage in all coverage areas of the mobile station's zone of lastregistration, and perhaps in adjacent zones to account for thepossibility that the mobile station has moved to a new zone without yetre-registering.

On the other hand, when a mobile station initiates a communication bytransmitting an access probe to the network via the access channel in agiven coverage area, the network may respond to that access probe bytransmitting a response message to the mobile station on a pagingchannel in the same coverage area. For instance, to initiate a call whenoperating in a given coverage area, a mobile station may transmit on anaccess channel of that coverage area an access probe that defines a callorigination request message. Upon receipt of that access probe, thenetwork may then carry out various call setup functions and may transmitto the mobile station on a paging channel of the coverage area achannel-assignment message that directs the mobile station to use aparticular air interface traffic channel to engage in the requestedcall, so that call may then begin.

If the coverage area on which the network receives a request message(e.g., call origination message) from a mobile station borders one ormore other coverage areas as is typical, the network may transmit aresponse to the mobile station not only in the coverage area in whichthe mobile station transmitted the request but also in each adjacentcoverage area, to account for the possibility that the mobile stationhas moved to another coverage area in the interim.

In a system where a wireless coverage defines more than one pagingchannel, a mechanism is typically provided for selecting a pagingchannel to use for paging particular mobile stations, preferably in amanner that evenly or at least randomly distributes paging channel loadamong the various mobile stations the coverage area at any given time.One way to accomplish this is through use of a hashing algorithm keyedto mobile station identifier. The hashing algorithm may take the form ofa probability function that, when applied to a given mobile station'sidentifier, will produce an index value that can be applied to a list ofpaging channels to indicate which paging channel should be used for thatmobile station.

For instance, the hashing algorithm applied to the mobile station'sidentifier may produce a value from 0 to 1. Assuming, by way of example,that there are four sequentially numbered paging channels in thecoverage area, a resulting value of 0 to 0.25 may then indicate thatpaging channel number 1 should be used, a resulting value of 0.26 to0.50 may indicate that paging channel number 2 should be used, aresulting value of 0.51 to 0.75 may indicate that paging channel number3 should be used, and a resulting value of 0.76 to 1.00 may indicatethat paging channel number 4 should be used. Of course, the number ofpaging channels may differ from this, the manner in which the hashresult would be applied to determine which paging channel to use for themobile station at issue may differ as well, and the hash function itselfmay take any of a variety of forms.

When a network pages a mobile station in a given coverage area that hasmore than one paging channel, the base station may apply the establishedhashing algorithm keyed to the mobile station's identifier to determinewhich paging channel to use for transmission of the page message to themobile station. Likewise, the mobile station may apply the same hashingalgorithm keyed to the mobile station's identifier to determine whichpaging channel to monitor for receipt of a page message destined to themobile station.

An overhead channel message (e.g., system-parameters message) that isbroadcast in each coverage area may specify how many paging channelsexist in the coverage area and may expressly or inherently define thepaging channels to facilitate this process. Depending on the airinterface protocol in use, for example, there may be a series ofpossible paging channels, and the overhead channel message may simplyspecify how many paging channels are defined for the coverage area, thusinherently indicating that the indicated number of paging channelsbeginning from the start of the sequence are in use.

In an example Code Division Multiple Access (CDMA) system, for instance,up to seven paging channels may be defined by spread spectrum modulationusing, respectively, “Walsh codes” 1 through 7. If the overhead channelmessage indicates that the coverage area has just one paging channel,for instance, that would constitute an inherent indication that thecoverage area has just paging channel #1, using Walsh code 1. Whereas,if the overhead channel message indicates that the coverage area has,say, three paging channels, then that would constitute an inherentindication that the coverage area has paging channels #1, #2, and #3,using Walsh codes 1, 2, and 3 respectively.

In this arrangement, or in analogous arrangements under other types ofair interface protocols, one paging channel may be considered a“primary” paging channel, typically because at least that paging channelwould be used in all (or substantially all) of the coverage areas in thesystem. Thus, each coverage area would employ the primary pagingchannel, and some or all of the coverage areas may also employ one ormore additional paging channels. The primary paging channel may bedefined with respect to a sequence of possible paging channels (e.g., asthe first channel of the sequence or the last of the sequence), as inthe CDMA example above for instance, or in any other manner.

OVERVIEW

When a mobile station moves from one coverage area into a coverage areathat has greater than one paging channel, the mobile station willgenerally apply the established hashing algorithm in order to determinewhich paging channel in the new coverage area the mobile station shouldmonitor for any page messages destined to the mobile station.Unfortunately, however, in the time that it takes the mobile station tofully “hash onto” a paging channel in the new coverage area (includingthe time that it takes the mobile station to learn from an overheadchannel message how many paging channels there are in the new coveragearea, and the time that it takes the mobile station to apply theestablished hashing algorithm to determine which paging channel tomonitor in the new coverage area), it is possible that the mobilestation may miss a page message transmitted to the mobile station in thenew coverage area. This can be a particular problem if the mobilestation is in an “access handoff” state, where the mobile station sentan access probe in one coverage area and is awaiting receipt of aresponse to the access probe when the mobile station enters the newcoverage area, since the mobile station may not receive the responsemessage in the new coverage area if the mobile station is busy hashingonto a paging channel in the new coverage area. Specifically if theaccess probe was a call origination message, the result of thissituation could be that a call attempt by the mobile station may fail,which may result in poor user experience.

One existing mechanism that is known to help to avoid this problem isfor the network to broadcast in a given coverage area an indication foreach neighboring coverage area of whether the neighboring coverage areahas the same number of paging channels as the given coverage area, andfor a mobile station to use that indication as a basis to decide whetherstay on the same paging channel that the mobile station was on the givencoverage area when it moves into an adjacent coverage area. Forinstance, in given coverage area, the network may broadcast or otherwiseprovide to served mobile stations a “neighbor list” that lists adjacentcoverage areas, primarily to allow the mobile stations to scan forpossible coverage of the adjacent coverage areas, and to facilitatehandoff. Such a neighbor list may specify (e.g., with a Boolean flag)for each listed neighboring coverage area whether or not the coveragearea has the same number of paging channels as the given coverage area.When a mobile station moves into a neighboring coverage area, the mobilestation may then have advanced knowledge of whether the neighboringcoverage area has the same number paging channels as the given coveragearea.

According to this known mechanism, if the indication is that theneighboring coverage area has the same number of paging channels as thegiven coverage area, then, when the mobile station moves to theneighboring coverage area, the mobile station may simply andautomatically stay on the same number paging channel that the mobilestation was monitoring in the given coverage area, which would be thesame channel that the mobile station would hash onto in any event. Inthis situation, the network may apply the established hashing algorithmas normal to determine which paging channel to use for paging the mobilestation in the neighboring coverage area, and the result should be thesame channel that the mobile station monitors, since the number ofpaging channels in the neighboring coverage area is the same as thenumber of paging channels in the given coverage area (where the hashingalgorithm may have been likewise applied).

On the other hand, if the neighboring coverage area has a differentnumber of paging channels than the given coverage area, then, when themobile station moves to the neighboring coverage area, the mobilestation may apply the established hashing algorithm to determine whichpaging channel in the neighboring coverage area the mobile stationshould use. And again conventionally, the network may also apply thehashing algorithm to determine which paging channel to use for pagingthe mobile station, and the result should match that obtained by themobile station.

Even with this known process, however, the mobile will still need tohash onto a paging channel in the neighboring coverage area if theneighboring coverage area has a different number of paging channels thanthe given coverage area. Therefore, in that scenario, there is still achance that the mobile station may miss a page message (e.g., anaccess-response message) that is sent to the mobile station in theneighboring coverage area while the mobile station is busy hashing ontothe appropriate paging channel in the neighboring coverage area.

Disclosed herein is a method, and correspondingly programmed apparatus,to help overcome this problem. In accordance with the method, when amobile station moves (or is moving or about to move) from a givencoverage area to a neighboring coverage area, if the numbers of pagingchannels in the two coverage areas differ, then the mobile station willautomatically select a default paging channel other than the pagingchannel that would result from applying the established hashingalgorithm. The default paging channel in this process may be the primarypaging channel (e.g., Walsh code 1, in an example CDMA system), but itcan be predefined in some other manner. Further, the network (e.g., abase station) will apply an analogous process to also select the defaultpaging channel for any page message that the network sends to the mobilestation in the neighboring coverage area.

This method applies particularly when the neighboring coverage area hasmore than one paging channel, since, if the neighboring coverage areahad just one paging channel that paging channel would of course be theone that the mobile station would select. In a scenario where theneighboring coverage area has a number of paging channels that isgreater than one and that is different than the number of pagingchannels in the given coverage area (from which the mobile station ismoving), the present method advantageously avoids the need for themobile station to go through the hashing process upon movement into theneighboring coverage area, as the mobile station will instead simplyselect the default paging channel by rote.

Further, the method can apply particularly when the default pagingchannel in the neighboring coverage area is different than the pagingchannel that the mobile station would hash onto in the neighboringcoverage area if the mobile station were to apply the establishedhashing algorithm. On the other hand, the method is also applicable in amore general sense with the mobile station selecting the default pagingchannel in the neighboring coverage area simply without applying thehashing algorithm and without considering an identifier of the mobilestation, even if the default paging channel would be the same as thepaging channel that the mobile station would select if the mobilestation were to apply the hashing algorithm. The advantage would be, inany event, that the mobile station would select a paging channel withoutthe need to go through the hashing function, and thus the mobile stationshould not miss a page message due to being busy hashing.

To support implementation of this method, the network may also bearranged to operate in a corresponding manner. For instance, if thenetwork is going to page the mobile station in a given coverage area andalso seeks to page the mobile station in a neighboring coverage area outof caution that the mobile station might have moved to the neighboringcoverage area, and if the neighboring coverage area has a number ofpaging channels that is greater than one and that is different than thenumber of paging channels in the given coverage area, then the networkmay simply page the mobile station on the default paging channel in theneighboring coverage area. Again in this scenario, the default pagingchannel would be a paging channel other than the paging channel thatwould be dictated by the established hashing algorithm.

The present method is especially useful when the mobile station is in anaccess handoff state. In that situation, the network would have receivedan access request transmitted by the mobile station in the givencoverage area and the network would transmit a response message both inthe given coverage area and in the neighboring coverage area, out ofcaution for the possibility that the mobile station had moved to theneighboring coverage area in the interim. In such a situation, thepresent method provides the advantage that the mobile station need notgo through the hashing process when entering into the neighboringcoverage area. The mobile station may simply monitor the default pagingchannel upon moving into the neighboring coverage area. Further, whenthe network has received an access request message from the mobilestation in a given coverage area and the network is going to send anaccess response message to the mobile station in a neighboring coveragearea, the network may correspondingly automatically transmit the accessresponse message on the default paging channel in the neighboringcoverage area.

By using the default paging channel for transmission/receipt of anaccess response message in the neighboring coverage area, the method maythus help to avoid a situation where the mobile station is busy hashingonto a paging channel (or has not yet selected a paging channel) in theneighboring coverage area and consequently fails to receive an accessresponse message transmitted in the neighboring coverage area.Therefore, the method may help to avoid access handoff failure.

In practice, however, if the mobile station will automatically monitorthe default paging channel upon moving into a neighboring coverage areaand the network will automatically transmit page messages to the mobilestation on the default paging channel when the mobile station moves intothe neighboring coverage area (or to safeguard for the possibility thatthe mobile station has moved into the neighboring coverage area), atleast two additional issues arise. First, by automatically using thedefault paging channel rather than the paging channel dictated by thehashing algorithm, the overall paging channel load may be more heavilyweighted on the default paging channel, defeating the load-balancinggoal of the hashing process. Second, the method would seem to requirethe network to know whether a given mobile station is applying themethod and particularly whether a given mobile station is currentlymonitoring the default paging channel rather than the paging channeldictated by the hashing algorithm.

To help overcome these additional issues, the method may be refined intwo respects. First, although the mobile station may decide through theabove process to monitor the default paging channel upon moving into aneighboring coverage area, the mobile station may be set to do so forjust a limited period of time and to then automatically switch over tomonitor the paging channel dictated by the hashing algorithm.Preferably, the period of time for which the mobile station monitors thedefault paging channel would be sufficient to allow the mobile stationto receive and process a response to an access request message that themobile station sent to the network before moving into the neighboringcoverage area, if the mobile station is in an access handoff state. Assuch, the period of time may be predefined by engineering design to besufficient for at least this purpose. Alternatively, the mobile stationmay simply monitor the default paging channel until the mobile stationactually receives a response to an access request message that themobile station sent before moving into the neighboring coverage area,and the mobile station may then switch over to monitor the pagingchannel dictated by the hashing algorithm.

Correspondingly, when the network has received an access request messagefrom the mobile station in a given coverage area and the network isgoing to send an access response message to the mobile station in aneighboring coverage area, as noted above the network may automaticallytransmit the access response message on the default paging channel inthe neighboring coverage area. After doing so, the network may thenautomatically switch over to use the paging channel dictated by thehashing algorithm for transmitting any further page messages to themobile station in the neighboring coverage area.

Second, given that the network may not know whether the mobile stationis in fact applying the method and whether the mobile station iscurrently monitoring the default paging channel rather the pagingchannel dictated by the hashing algorithm, the method may beadditionally refined to have the network page the mobile stationconcurrently on both the default paging channel and the paging channeldictated by the hashing algorithm. Thus, when the network has receivedan access request message from the mobile station in a given coveragearea and the network is going to send an access response message to themobile station in a neighboring coverage area, the network mayautomatically transmit the access response message on both the defaultpaging channel in the neighboring coverage area and the paging channeldictated by the hashing algorithm in the neighboring coverage area. Thatway, absent other issues, the mobile station should receive the accessresponse message regardless of whether the mobile station is monitoringthe default paging channel or the channel dictated by the hashingalgorithm.

In a preferred implementation, the network may limit application of thisrefined method to scenario where the mobile station is likely in anaccess handoff state. To do so, when the network is going to transmit anaccess response message to a mobile station in a particular coveragearea, the network may determine whether the access response message is aresponse to an access request message that the network received in thesame coverage area. If so, then the network may conclude that the accessresponse message is not being sent in an access handoff scenario, since,if the mobile station is still in the coverage area where the mobilestation sent the access request message, the mobile station wouldalready be monitoring the paging channel dictated by the hashingalgorithm in that coverage area. Thus, in that scenario, the network maysimply transmit the access response message to the mobile station on thepaging channel dictated by the hashing algorithm. On the other hand, ifthe network determines that the access response message beingtransmitted in a particular coverage area is a response to an accessrequest message that the network received in another coverage area, thenthe network may conclude that the access response message is being sentin an access handoff scenario. In that case, the network may thentransmit the access response message concurrently (i.e., at the sametime or substantially the same time) on both the default paging channeland the paging channel dictated by the hashing algorithm.

In practice, these refined network functions can be implemented by abase station in the network. In particular, if and when the base stationreceives from a mobile station an access request message in a coveragearea (e.g., a specific cell sector), the base station may record thatfact. In turn, when the base station encounters a need to transmit anaccess response message to the mobile station in particular coveragearea (e.g., where the response message is generated by the base stationor is provided to the base station by other network infrastructure suchas a base station controller or switch), the base station may determinewhether the base station had received in the particular coverage areathe access request message to which the response is a response. If so,then the base station may conclude that the response message is notbeing sent in an access handoff scenario, and the base station maytherefore transmit the response message in the particular coverage areaon the paging channel dictated by the hashing algorithm. On the otherhand, if the base station determines that the base station had receivedin the particular coverage area the access request message to which theresponse is a response, then the base station may conclude that theresponse message is being sent in an access handoff scenario, and so thebase station may transmit the response message in the particularcoverage area on both the default paging channel and the paging channeldictated by the hashing algorithm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a cellular wirelesscommunication system in which an exemplary embodiment of the presentmethod can be implemented.

FIG. 2 is a flow chart depicting functions that can be carried out by amobile station in accordance with the exemplary method.

FIG. 3 is another flow chart depicting functions that can be carried outby a mobile station in accordance with the exemplary method.

FIG. 4 is a flow chart depicting functions that can be carried out by aRAN in accordance with the exemplary method.

FIG. 5 is another flow chart depicting functions that can be carried outby a RAN in accordance with the exemplary method.

FIG. 6 is another flow chart depicting functions that can be carried outby a RAN in accordance with the exemplary method.

FIG. 7 is a simplified block diagram of a mobile station operable in theexemplary method.

FIG. 8 is a simplified block diagram of a base station operable in theexemplary method.

DETAILED DESCRIPTION

The present method will now be described with reference to the figures.It should be understood, however, that numerous variations from thearrangement and functions shown are possible while remaining within thescope and spirit of the claims. For instance, elements may be added,removed, combined, distributed, substituted, re-positioned, re-ordered,or otherwise changed. Further, where this description refers tofunctions being carried out by an entity such as a mobile station or abase station (or other network component), it will be understood thatthe entity can carry out the functions by itself or with the assistanceof other entities, and through application of hardware, firmware and/orsoftware logic. For instance, the entity may include a processorprogrammed with instructions to implement the functions described. Stillfurther, it should be understood that all of the discussion above isconsidered part of this detailed disclosure.

Referring to the drawings, as noted above, FIG. 1 is a simplified blockdiagram of a cellular wireless communication system in which the presentmethod can be implemented. The system includes at its core a radioaccess network (RAN) 12 that functions to provide served mobile stationswith communication service, such as access to one or more transportnetworks 14 for instance. As shown, the example RAN 12 includes one ormore base stations (BSs) 16, one or more base station controllers (BSCs)18, and one or more switches/gateways 20 providing connectivity withtransport networks 14. A suitable RAN can take other forms as well,ranging in degree of complexity and scope of operation.

Each base station preferably includes one or more antenna arrangementsand associated equipment for radiating to define one or more wirelesscoverage areas, such as cell sectors for instance, in which mobilestations may operate. FIG. 1 depicts two representative coverage areas22, 24 by way of example. These two coverage areas may emanate from acommon base station or may emanate from separate base stations. In eachcoverage area, communications between the serving base station andserved mobile stations may be compliant with one or more air interfaceprotocols, example of which include CDMA (e.g., 1xRTT, 1xEV-DO), iDEN,WiMAX (e.g., IEEE 802.16), LTE, TDMA, AMPS, GSM, GPRS, UMTS, or EDGE,WI-FI (e.g., IEEE 802.11), BLUETOOTH, and others now known or laterdeveloped.

Shown operating in coverage area 22 and moving from coverage area 22 tocoverage area 24 is an example mobile station 26, operable to be servedby RAN 12. Mobile station 26 may be a cellular telephone, wirelesslyequipped personal digital assistant or personal computer, or otherwirelessly equipped device. Although the term “mobile station” is usedby convention to describe such a device, it is understood that thedevice need not actually be movable. Mobile station 26 could in theorybe fixed in position. In that case, the “movement” of mobile station 26from coverage area 22 to coverage area 24 could be an idle or activehandoff of mobile station 26 resulting from change in the relative airinterface conditions of the two coverage areas or from other factorsbeyond mere physical movement of the device itself. Preferably, mobilestation 26 has a unique identifier such as a mobile identificationnumber (MIN), mobile directory number (MDN), international mobilesubscriber identifier (IMSI), or the like, which can be used as a basisto target page messages to the mobile station and for other purposes.

In general, as discussed above, each coverage area 22, 24 defines anumber of paging channels through which the RAN can transmit pagemessages targeted to specific mobile stations. Specifics of how thesepaging channels are defined will vary depending on air interfaceprotocol will be understood by both the RAN and the served mobilestations so that the RAN can transmit a page message to a specificmobile station and the mobile station can receive and process the pagemessage.

As one example, each paging channel may define periodically recurringtimeslots for carrying page messages. When a mobile station monitors apaging channel in search of a page message, the mobile station may scantimeslots of the paging channel at a periodic interval defining a slotcycle, and the mobile station may determine whether the paging channelcarries a page message indicating the mobile station's identifier. Ifso, the mobile station may then process the page message as a messagedestined to the mobile station.

Preferably in each coverage area, the serving base station willbroadcast a specification of paging channels defined in the coveragearea, so that a mobile station beginning to operate in the coverage areacan determine how many paging channels the coverage area includes and,if more than one, can determine which paging channel to monitor. By wayof example, this specification may be an indication in a systemparameters message that the base station broadcasts periodically orrepeatedly on an overhead channel. Further, the specification may definethe paging channels expressly by particular coding parameters or, asnoted above may simply indicate how many paging channels there are,which may inherently define the paging channels if a sequence ofpossible paging channels exists.

Preferably, all of the coverage areas in a given system will have aprimary paging channel, which may be used as the “default” pagingchannel in the present method. For instance, in an example CDMA systemas discussed above, there may be a sequence of possible paging channels,with a sequence of Walsh codes used for spread spectrum modulation todefine respective paging channels. In such an arrangement, the primarypaging channel may be defined by Walsh code 1 in each coverage area. Buteach coverage area may then have one or more additional paging channels.

To generalize, coverage area 22 is shown having M paging channels, andcoverage area 24 is shown having N paging channels. In practice, thecoverage areas may have the same number of paging channels, in whichcase M would equal N. Alternatively, the coverage areas may have adifferent number of paging channels, in which case M would not equal N.Preferably, the number N of paging channels in coverage area 24 intowhich mobile station 26 is moving is greater than one, i.e., there areat least two paging channels in coverage area 24. As such, coverage area24 would include the primary (default) paging channel and at least oneadditional paging channel. On the other hand, the number M of pagingchannels in coverage area 22, may be one or more, and so coverage area22 would include the primary paging channel and may include one or moreadditional paging channels.

For purposes of paging in a coverage area that includes more than onepaging channel, the serving RAN (e.g., the serving base station) andeach served mobile station are preferably programmed to apply a commonhashing algorithm to determine which paging channel will be used. Inparticular, when the RAN has a page message to send to mobile station ina coverage area that defines more than one paging channel, the RAN willapply the hashing algorithm with respect to the mobile station'sidentifier to produce a result that will indicate which paging channelis to be used, and the RAN will then transmit the page message to themobile station on that paging channel. At the same time, when a mobilestation is to scan for a page message, the mobile station will apply thesame hashing algorithm with respect to its identifier, to produce thesame result that will indicate the same paging channel to be used, andthe mobile station will then scan that paging channel for an incomingpage message.

The hashing algorithm established for use in a given system can take anyof a variety of forms, but preferably (although not necessarily) resultsin a random enough distribution of paging load among the availablepaging channels in a given coverage area. By way of example, the wellknown SHA-1 algorithm could be used as the hashing algorithm. Otherexamples, now known or later developed, may be possible as well.

For purposes of description in this document, the paging channel thatwould be selected in a given coverage area by applying the establishedhashing algorithm keyed to the target mobile station's identifier (i.e.,the paging channel that would be dictated by the hashing algorithm) maybe considered the “ID-hash channel” for that mobile station in thatcoverage area. In some coverage areas, the mobile station's ID-hashchannel may be the primary paging channel, but in other coverage areas,the mobile station's ID-hash channel may be another paging channel.

As further noted above, the present method is especially useful in thecontext of access handoff, particularly where a mobile station movesfrom one coverage area to another while the mobile station is seeking toinitiate a call (e.g., voice call or data communication session). In thearrangement of FIG. 1, for instance, this may occur if mobile station 26sends an access probe defining a call origination request to RAN 12while in coverage area 22 and mobile station 26 moves into coverage area24 before receiving a response to that access request message. Optimallyas noted above, when RAN 12 is going to transmit an access response tomobile station 26, RAN 12 would transmit the response not only incoverage area 22 where RAN 12 receives the access request but also inneighboring coverage area 24, to safeguard for the possibility thatmobile station 26 moved to coverage area 24 after sending the accessrequest message. In that scenario, the present method may help to ensurethat the mobile station receives the access response message in coveragearea 24, as the method may help to avoid communication of the accessresponse message during the time when the mobile station is hashing ontoa paging channel in coverage area 24 (e.g., determining how many pagingchannels exist in coverage area 24 and, if more than one, applying thehashing algorithm to determine which of the paging channels to monitor).

FIG. 2 is a flow chart depicting how this may occur in practice inaccordance with an embodiment of the method. As shown in FIG. 2, atblock 30, mobile station 26 operates in coverage area 22, monitoring apaging channel in coverage area 22 in search of any page messagedestined to the mobile station. If coverage area 22 has more than onepaging channel, we can assume that mobile station 26 was monitoring itsID-hash channel in coverage area 22, and that RAN 12 would page mobilestation 26 on that ID-hash channel in coverage area 22 if the RAN had apage message to send to the mobile station. For instance, if the mobilestation initially powered-on in coverage area 22 or the mobile stationmoved into coverage area 22 from another coverage area, mobile station26 may have determined from an overhead channel message how many pagingchannels are defined in coverage area 22, and mobile station 26 may havethen applied the established hashing algorithm keyed to the mobilestation's identifier in order to determine which of the paging channelsin coverage area 22 to monitor. Mobile station 26 may then “idle” on theselected paging channel in coverage area 22, in that mobile stationmonitors the selected paging channel to await receipt of a page message(e.g., a page message responding to an access request message from themobile station, or another page message) from the RAN.

At block 32, mobile 26 then moves from coverage area 22 to coverage area24. Although mobile station 26 may be in an area of overlap between thecoverage areas at this point and may thus be able to communicate withthe RAN in both coverage areas, the act of the mobile station movingfrom one coverage area to another relates to the mobile stationswitching from monitoring a paging channel in one coverage area tomonitoring a paging channel in the other coverage area. Thus, at issuewould then be which paging channel mobile station 26 should monitor incoverage area 24 upon moving into coverage area 24.

To help resolve this issue, at block 36, the mobile station willdetermine whether the number of paging channels in coverage area 36 isdifferent than the number of paging channels in coverage area 22. Themobile station may make this determination in various ways. For example,when mobile station 26 was operating in coverage area 22, the mobilestation would likely have determined how many paging channels there werein coverage area 22, and the mobile station may have recorded thatnumber in its memory. When mobile station 26 moves into coverage area24, the mobile station may then read a system parameters message or thelike to determine the number of paging channels in coverage area 24 andmay compare that number with the number of paging channels in coveragearea 22 that the mobile station recorded in its memory, to determine ifthe numbers are different. As another example, as noted above, the RANmay have transmitted to mobile station 26 a neighbor list or other suchmessage that included a flag indicating whether coverage area 24 has thesame number of paging channels as coverage area 22, and mobile station26 may thus refer to that indication to determine if the numbers aredifferent.

If mobile station 26 determines at block 36 that the number of pagingchannels in coverage area 24 is different than the number of pagingchannels in coverage area 22, then, at block 38, mobile station 26 willselect by rote (automatically) the default paging channel, and themobile station may idle on the default paging channel in coverage area24. Preferably, the default paging channel thus selected will bedifferent than the mobile station's ID-hash channel in coverage area 24.However, as noted above, it is possible that the mobile station'sID-hash channel could be the same as the default paging channel. Animportant point is that, when the mobile station faces a situation wherethe number of paging channels in coverage area 24 is different than thenumber of paging channels in coverage area 22, the mobile station willautomatically operate on the default paging channel (e.g., the primarypaging channel) in coverage area 24 without first applying the hashingalgorithm to select the paging channel.

On the other hand, if the mobile station determines at block 36 that thenumber of paging channels in coverage area 24 is the same as the numberof paging channels in coverage area 22, then, at block 40, the mobilestation may simply select in coverage area 24 the same paging channelthat the mobile station was monitoring in coverage area 22, and themobile station may idle on that selected paging channel in coverage area24. As noted above, the paging channel thereby selected by rote wouldlikely be the ID-hash channel, assuming the mobile station has appliedthe hashing algorithm to select the paging channel on which the mobilestation idled in coverage area 22.

As further noted above, this method can be especially useful in anaccess handoff scenario. Indeed, the method can be conditioned on themobile station being in an access handoff state. This variation is shownby dashed block 34 (which may or may not be optional) in FIG. 2. Inparticular, upon moving into coverage area 22, mobile station 26determines at block 34 whether mobile station 26 is in an access handoffstate. For instance, mobile station 26 may simply determine if ittransmitted an access request message in coverage area 22 and it stillawaits receipt of an access response message from the RAN. If so, thenmobile station 26 may proceed to block 38 of FIG. 2 as discussed above.Otherwise, the process may end, as the mobile station is not in anaccess handoff state.

Furthermore, as also noted above, in a scenario where the mobile stationapplies the above process and thereby opts by rote to idle on thedefault paging channel when coverage area 24 has a different number ofpaging channels than coverage area 22, the mobile station may idle onthe default paging channel for a particular period of time and may thenautomatically switch over to idle on the mobile station's ID-hashchannel. As explained above, if the network correspondingly pages themobile station on the ID-hash channel after that particular period oftime, then the load balancing function of the hashing algorithm canoptimally apply. This switch of paging channels is depicted by dashedblock 42 (which may or may not be optional), where, after the mobilestation has idled on the default paging channel in coverage area 24 fora particular period of time, the mobile station automatically switchesover to idle on its ID-hash channel in coverage area 24. As noted above,the period of time that the mobile station idles on the default pagingchannel may be a predefined period of time, preferably a time periodthat is set by engineering design to be sufficient for the mobilestation to receive from the RAN a response to an access request messagethat the mobile station may have sent while in coverage area 22.Alternatively, the period of time may be dynamically extend until themobile station receives such an access response message, or until theearlier of such receipt and a predefined expiration time. Otherarrangements are possible as well.

FIG. 3 is another flow chart depicting functions that can be carried outby a mobile station, such as mobile station 26, in accordance with thepresent method. As shown in FIG. 3, at block 50, the mobile station maypower-on in a first coverage area that has a first quantity of pagingchannels. At block 52, upon powering-on, the mobile station may thenreceive from a RAN via the first wireless coverage area an overheadmessage that specifies the first quantity of paging channels. And atblock 54, assuming the first wireless coverage area has more than onepaging channel, the mobile station may then apply a hashing algorithmkeyed to the mobile station's identifier, to select one of the pagingchannels of the first wireless coverage area. At block 56, the mobilestation may then idle on the selected paging channel of the firstwireless coverage area to await receipt of a paging channel message(i.e., a page message) in the first wireless coverage area.

At block 58, while the mobile station is powered-on, the mobile stationmay then move from a second wireless coverage area that has a secondquantity of paging channels into a third wireless coverage area that hasa third quantity of paging channels greater than one. At block 60, themobile station may then make a determination of whether the thirdquantity is the same as the second quantity. If the determination isthat the quantities are the same, then, at block 62, the mobile stationmay select and idle on the same paging channel in the third wirelesscoverage area that the mobile station was idling on in the secondwireless coverage area just before moving into the third wirelesscoverage area. On the other hand, if the determination is that thequantities are different, then, at block 64, the mobile station mayselect by rote and idles on a default paging channel in the thirdwireless coverage area, i.e., without taking into consideration (inselecting the channel) the mobile station's identifier and withouttaking into consideration which paging channel the mobile station wasidling on in the second wireless coverage area just before moving intothe third wireless coverage area.

In this process, the default paging channel may be a primary pagingchannel. Further, the default paging channel is preferably differentthan the paging channel that the mobile station would have idled on inthe third coverage area in a scenario where the determination is thatthe third quantity is the same as the second quantity.

Furthermore, in this process, the “second” wireless coverage area may bethe “first” wireless coverage area and the “first” quantity may be the“second quantity”. In that case, the act of the mobile station movingfrom the second wireless coverage area to the third wireless coveragearea may be the mobile station moving from the first wireless coveragearea to the third wireless coverage area. With application of themethod, the mobile station may thus have powered on in the firstwireless coverage area and applied the hashing algorithm to select apaging channel on which to idle in the first wireless coverage area, andthe mobile station may then move from the first wireless coverage areato the third wireless coverage area and, in view of the difference innumber of paging channels between the two wireless coverage areas,decide by rote to idle on the default paging channel in the thirdwireless coverage area.

In addition, as discussed above, the method may additionally involve themobile station idling on the rote-selected default paging channel in thethird wireless coverage area for a particular (e.g., predefined) periodof time and then automatically switching over to idle in the thirdwireless coverage area on a paging channel selected based on the hashingalgorithm keyed to the mobile station's identifier.

FIG. 4 is next a flow chart depicting functions that can be carried outby RAN (e.g., a base station 16) in accordance with the exemplarymethod. As shown in FIG. 4, at block 70, the RAN encounters a situationwhere the RAN is to page the mobile station in a given coverage areasuch as coverage area 22. To safeguard for the possibility that mobilestation has moved from coverage area 22 to coverage area 24, however,the RAN may also page the mobile station in coverage area 24. Theassumption in this situation is that coverage area 24 has more than onepaging channel. Thus, at issue is which paging channel the RAN shoulduse to page the mobile station in coverage area 24.

To help resolve this issue, at block 72, the RAN will determine whetherthe number of paging channels in coverage area 24 is different than thenumber of paging channels in coverage area 22. If the determination isthat the number of paging channels in coverage area 24 is different thanthe number of paging channels in coverage area 22, then, at block 74,the RAN may select and use the default (e.g., primary) paging channel incoverage area 24, preferably where the default paging channel isdifferent than the mobile station's ID-hash channel. On the other hand,if the determination is that the number of paging channels in coveragearea 24 is the same as the number of paging channels in coverage area22, then, at block 76, the RAN may select and use the mobile station'sID-hash channel in coverage area 24.

As with the mobile station method above, this process implemented by theRAN can be limited to an access handoff scenario. This variation isillustrated by FIG. 5. As shown in FIG. 5, at block 82, the RANencounters a situation where the RAN is to transmit a page message tothe mobile station in coverage area 24. At block 84, the RAN thendetermines whether the page message is being transmitted to the mobilestation in an access handoff scenario. In particular, the RAN determineswhether the page message is an access response message and is a responseto an access request message that the RAN received from the mobilestation in a different coverage area.

In practice, for instance, this function may be carried out by a basestation 16 that serves coverage area 24, when the base station receivesfrom a BSC 18 or other RAN infrastructure a directive to transmit thepage message to the mobile station in coverage area 24. Upon receipt ofthat directive, the base station 16 may read the header information(e.g., a message type indicator) in the page message that indicateswhether the page message is an access response message (e.g., a channelassignment message). Further, the base station 16 may consult its memoryto determine whether the base station received the corresponding accessrequest message from the mobile station in the same coverage area 24.

If the RAN thereby determines that the page message being transmitted tothe mobile station is an access response message and is a response to anaccess request message that the RAN received from the mobile station ina different coverage area, then the RAN may conclude that the pagemessage is being transmitted to the mobile station in an access handoffscenario. In that case, the RAN would proceed to apply the aboveprocess. In particular, at block 86, the would determine whether thenumber of paging channels in coverage area 24 is different than thenumber of paging channels in the coverage area where the RAN receivedthe corresponding access request message, e.g., coverage area 22. If thedetermination is that the number of paging channels in coverage area 24is different than the number of paging channels in the coverage areawhere the RAN received the corresponding access request message, then,at block 88, the RAN would select and use the default paging channel incoverage area 24 to transmit the access response message to the mobilestation. On the other hand, if the determination is that the number ofpaging channels in coverage area 24 is the same as the number of pagingchannels in the coverage area where the RAN received the access requestmessage, then, at block 90, the RAN may select and use the mobilestation's ID-hash channel in coverage area 24 to transmit the accessresponse message to the mobile station.

On the other hand, if the RAN determines at block 84 that the pagemessage being transmitted to the mobile station is not being transmittedin an access handoff scenario, then the RAN may forego carrying out theabove process. Instead, at block 92, the RAN may simply select and usethe mobile station's ID-hash channel to transmit the page message to themobile station in coverage area 24, or the RAN may take some othermeasure.

As also discussed above, in an access handoff scenario (or for thatmatter in some other scenario), the RAN may advantageously transmit apage message to the mobile station in a given coverage area on both thedefault paging channel (different than the mobile station's ID-hashchannel) and the mobile station's ID-hash channel. FIG. 6 illustratesthis process by way of example.

As shown in FIG. 6, at block 100, the RAN encounters a situation wherethe RAN is to transmit a page message to the mobile station in coveragearea 24. At block 102, the RAN then determines whether the page messageis being transmitted to the mobile station in an access handoffscenario. In particular, the RAN determines whether the page message isan access response message and is a response to an access requestmessage that the RAN received from the mobile station in a differentcoverage area.

As discussed above, this function may be carried out by a base station16 that serves coverage area 24, when the base station receives from aBSC 18 or other RAN infrastructure a directive to transmit the pagemessage to the mobile station in coverage area 24. Upon receipt of thatdirective, the base station 16 may read the header information (e.g., amessage type indicator) in the page message that indicates whether thepage message is an access response message (e.g., a channel assignmentmessage). Further, the base station 16 may consult its memory todetermine whether the base station received the corresponding accessrequest message from the mobile station in the same coverage area 24.

If the RAN thereby determines that the page message being transmitted tothe mobile station is an access response message and is a response to anaccess request message that the RAN received from the mobile station ina different coverage area, then the RAN may conclude that the pagemessage is being transmitted to the mobile station in an access handoffscenario. In that case, at block 104, the RAN would transmit the pagemessage to the mobile station in coverage area 24 on both the defaultpaging channel (different than the mobile station's ID-hash channel) andthe mobile station's ID-hash channel. Advantageously, this shouldincrease the chances of the mobile station receiving the page message,particularly in a scenario where the RAN does not know if the mobilestation is monitoring the default paging channel or the ID-hash channel.

On the other hand, if the RAN determines at block 102 that the pagemessage being transmitted to the mobile station in coverage area 24 isnot being transmitted in an access handoff scenario (e.g., that the pagemessage is not an access response message or that the RAN received thecorresponding access request message in coverage area 24 as well), then,at block 106, the RAN would transmit the page message to the mobilestation on the mobile station's ID-hash channel.

Also as with the mobile station method above, the RAN can be set to usethe rote-selected default paging channel for a defined period of timeand to then switch over to use the mobile station's ID-hash channel.From the RAN's perspective, these settings would be in place for anypage messages that the RAN needs to send to the mobile station incoverage area 24. For instance, in an access handoff scenario asdiscussed above, if the RAN determines that the number of pagingchannels in coverage area 24 is different than the number of pagingchannels in the coverage area where the RAN received the correspondingaccess request message, then the RAN may set itself to use the defaultpaging channel for transmission of any page messages to the mobilestation for a period of time, and the RAN may then automatically re-setitself to use the mobile station's ID-hash channel for transmission ofany page messages to the mobile station after that period of time.

This variation is depicted by the dashed boxes in FIGS. 4-6. Inparticular, in FIG. 4, at block 78 (following block 74), the RAN may beset to use the default paging channel in coverage area 24 fortransmission of any page messages to the mobile station for a definedperiod of time, and at block 80 the RAN may then automatically setitself to use the mobile station's ID-hash channel in coverage area 24for transmission of any page messages to the mobile station. Likewise,in FIG. 5, at block 94 (following block 88), the RAN may be set to usethe default paging channel in coverage area 24 for transmission of anypage messages to the mobile station for a defined period of time, and atblock 96, the RAN may then automatically set itself to use the mobilestation's ID-hash channel in coverage area 24 for transmission of anypage messages to the mobile station. Further, in FIG. 6, at block 108(following block 104), the RAN may be set to use both the default pagingchannel and the ID-hash channel in coverage area 24 for transmission ofany page messages to the mobile station for a defined period of time,and, at block 110, the RAN may then automatically set itself to use justthe mobile station's ID-hash channel in coverage area 24 fortransmission of any page messages to the mobile station.

FIG. 7 is next a simplified block diagram of an exemplary mobile station26, showing functional components that can be included in such a device.As shown, the exemplary mobile station includes a wireless communicationinterface 120, a user interface 122, a processor 124, and data storage126, all of which may be communicatively linked together by a systembus, network, or other connection mechanism 128. The mobile station maytake other forms as well.

Wireless communication interface 120 (including an antenna, not shown)functions to facilitate air interface communication with RAN 12according to one or more protocols such as those noted above. Userinterface 122 includes components for receiving input from a user ofmobile station and providing output to a user of the mobile station.Processor 124 may comprise one or more processors (e.g., general purposeand/or special purpose processors), such as microprocessors forinstance. And data storage 126 may comprise one or more volatile and/ornon-volatile storage components, such as magnetic, optical, or organicstorage components, and may be integrated in whole or in part withprocessor 124. As further shown, data storage 126 preferably containsprogram logic (e.g., machine language instructions) 130 executable byprocessor 124 to carry out various mobile station functions describedherein.

FIG. 8 is next a simplified block diagram of an exemplary base station16, showing functional components that can be included in such a device.As shown, the exemplary base station 16 includes an antenna structure132, a backhaul interface 134, a processor 136, and data storage 138,all of which may be communicatively linked together by a system bus,network, or other connection mechanism 140. The base station may takeother forms as well. Further, the base station may be a macro networkbase station, a femtocell base station, or any other type of basestation now known or later developed.

Antenna structure 132 (including a power amplifier, not shown),functions to facilitate air interface communication with served mobilestations, such as mobile station 26, according to one or more protocolssuch as those noted above. Backhaul interface 134 functions to provide aconnection with other RAN infrastructure, such as with a BSC 18 forinstance. As such, backhaul interface 134 may include a networkinterface module arranged to couple with or provide a wired or wirelessbackhaul connection. Processor 136 may comprise one or more processors(e.g., general purpose and/or special purpose processors), such asmicroprocessors for instance. And data storage 138 may comprise one ormore volatile and/or non-volatile storage components, such as magnetic,optical, or organic storage components, and may be integrated in wholeor in part with processor 136. As further shown, data storage 138preferably contains program logic (e.g., machine language instructions)142 executable by processor 136 to carry out various RAN functions(e.g., base station functions) described herein.

Exemplary embodiment of the present invention has been described above.Those of ordinary skill in the art will appreciate, however, thatnumerous changes may be made from the embodiments described withoutdeviating from the scope of the invention as defined by the claims.

1. A mobile station operable within wireless coverage of a radio accessnetwork (RAN), the mobile station having an identifier, the RANradiating to define a plurality of wireless coverage areas including afirst wireless coverage area having a first quantity of paging channelsand a second wireless coverage adjacent to the first wireless coveragearea and having a second quantity of paging channels greater than one,the mobile station comprising: a wireless transceiver operable to engagein air interface communication with the RAN, the mobile station beingarranged such that when the mobile station powers-on in the secondwireless coverage area, the mobile station applies a hashing algorithmkeyed to its identifier to select a given one of the second coveragearea's paging channels and the mobile station idles on the selectedgiven paging channel in the second wireless coverage area to awaitreceipt of a paging channel message from the RAN, the mobile stationbeing further arranged such that, when the mobile station is powered-onand moves from the first wireless coverage area to the second wirelesscoverage area, the mobile station applies a default paging channelselection process by which (i) the mobile station makes a determinationof whether the second quantity is the same as the first quantity, (ii)if the determination is that the second quantity is the same as thefirst quantity, then the mobile station selects and idles on the samepaging channel in the second wireless coverage area that the mobilestation was idling on in the first wireless coverage area just beforemoving into the second wireless coverage area and (iii) if thedetermination is that the second quality is different than the firstquantity, then the mobile station selects by rote and idles on a defaultpaging channel in the second wireless coverage area without taking intoconsideration the mobile station's identifier and without taking intoconsideration which paging channel the mobile station was idling on inthe first wireless coverage area just before moving into the secondwireless coverage area, wherein the default paging channel is differentthan the paging channel the mobile station would idle on in the secondcoverage area if the determination is that the second quality is thesame as the first quantity.
 2. The mobile station of claim 1, whereinthe default paging channel is other than the given paging channel. 3.The mobile station of claim 2, wherein the mobile station is a cellulartelephone.
 4. The mobile station of claim 2, wherein the mobile stationis arranged to condition application of the default paging channelselection process on the mobile station being in an access handoff statein which the mobile station sent an access request to the RAN in thefirst wireless coverage area and the mobile station then moved to thesecond wireless coverage area before receiving a corresponding accessresponse message from the RAN.
 5. The mobile station of claim 2, whereinif the mobile station applies the default paging channel selectionprocess and thereby selects the default paging channel on which to idle,the mobile station also applies the hashing algorithm keyed to itsidentifier to select the given one of the second coverage area's pagingchannels, and the mobile station idles on the default paging channel inthe second wireless coverage area for a particular period of time andthen automatically switches over to idle on the given paging channel inthe second wireless coverage area.
 6. The mobile station of claim 2,further comprising: a processor; data storage; and program logic storedin the data storage and executable by the processor to apply the hashingalgorithm to select the given paging channel when the mobile stationpowers on in the second coverage area, and to apply the default pagingchannel selection process when the mobile station moves from the firstwireless coverage area to the second wireless coverage area.
 7. Themobile station of claim 2, wherein the first coverage area is a cellsector, and wherein the second coverage area is another cell sector. 8.The mobile station of claim 2, wherein the mobile station receives fromthe RAN, via the wireless transceiver, a first overhead messagespecifying the quantity of paging channels in the first wirelesscoverage area, wherein the mobile station receives from the RAN, via thewireless transceiver, a second overhead message specifying the quantityof paging channels in the second wireless coverage area, and wherein themobile station determines if the second quantity is the same as thefirst quantity by comparing the specified quantities.
 9. The mobilestation of claim 2, wherein, when the mobile station is in the firstcoverage area, the mobile station receives via the wireless transceiverfrom the RAN a neighbor list providing a specification of whether thesecond coverage area has the same quantity of paging channels as thefirst coverage area, and wherein the mobile station determines if thesecond quantity is the same as the first quantity by referring to thespecification included in the neighbor list.
 10. The mobile station ofclaim 2, wherein the default paging channel is a primary paging channel.11. A method carried out by a mobile station, the mobile station havingan identifier, the method comprising: powering-on in a first wirelesscoverage area that has a first quantity of paging channels; uponpowering-on, (i) receiving an overhead message transmitted from a radioaccess network (RAN) via the first wireless coverage area, the overheadmessage specifying the first quantity of paging channels, and (ii)applying a hashing algorithm keyed to the mobile station's identifier,to select one of the paging channels of the first wireless coveragearea, and (iii) idling on the selected paging channel of the firstwireless coverage area to await receipt of a paging channel message inthe first wireless coverage area; while powered-on, (i) moving from asecond wireless coverage area into a third wireless coverage area,wherein the second wireless coverage area has a second quantity ofpaging channels, and wherein the third wireless coverage area has athird quantity of paging channels, (ii) making a determination ofwhether the third quantity is the same as the second quantity, (iii) ifthe determination is that the third quantity is the same as the secondquantity, then selecting and idling on the same paging channel in thethird wireless coverage area that the mobile station was idling on inthe second wireless coverage area just before moving into the thirdwireless coverage area, and (iv) if the determination is that the thirdquantity is different than the second quantity, then selecting by roteand idling on a default paging channel in the third wireless coveragearea without taking into consideration the mobile station's identifierand without taking into consideration which paging channel the mobilestation was idling on in the second wireless coverage area just beforemoving into the third wireless coverage area, wherein the default pagingchannel is different than the paging channel the mobile station wouldidle on in the third coverage area if the determination is that thethird quantity is the same as the second quantity.
 12. The method ofclaim 11, wherein the second wireless coverage area is the firstwireless coverage area and the first quantity is the second quantity,and so the mobile station moving from the second wireless coverage areato the third wireless coverage area is the mobile station moving fromthe first wireless coverage area to the third wireless coverage area.13. The method of claim 11, wherein idling by rote on the default pagingchannel in the third wireless coverage area comprises: idling on thedefault paging channel in the third wireless coverage area for aparticular period of time, and then automatically switching over to idlein the third wireless coverage area on a paging channel selected basedon the hashing algorithm keyed to the mobile station's identifier. 14.The method of claim 11, wherein the default paging channel is a primarypaging channel.